Abstract
Contact with Leishmania leads to a decreases in mononuclear phagocyte adherence to connective tissue. In this work, we studied the early stages of bond formation between VLA4 and fibronectin, measured the kinetics of membrane alignment and the monocyte cytoplasm spreading area over a fibronectin-coated surface, and studied the expression of high affinity integrin epitope in uninfected and Leishmania-infected human monocytes. Our results show that the initial VLA4-mediated interaction of Leishmania-infected monocyte with a fibronectin-coated surface is preserved, however, the later stage, leukocyte spreading over the substrate is abrogated in Leishmania-infected cells. The median of spreading area was 72 [55–89] μm2 for uninfected and 41 [34–51] μm2 for Leishmania-infected monocyte. This cytoplasm spread was inhibited using an anti-VLA4 blocking antibody. After the initial contact with the fibronectrin-coated surface, uninfected monocyte quickly spread the cytoplasm at a 15 μm2 s−1 ratio whilst Leishmania-infected monocytes only made small contacts at a 5.5 μm2 s−1 ratio. The expression of high affinity epitope by VLA4 (from 39 ± 21% to 14 ± 3%); and LFA1 (from 37 ± 32% to 18 ± 16%) molecules was reduced in Leishmania-infected monocytes. These changes in phagocyte function may be important for parasite dissemination and distribution of lesions in leishmaniasis.
Highlights
Infection with Leishmania downregulates the expression of the genes encoding the chemokine receptors CCR4 and CCR5 in murine inflammatory macrophages and the genes encoding CCR2 and CCR5 in murine dendritic cells[5,6]
After Mn++ stimulation, the frequency of arrests increased in both uninfected and Leishmania-infected monocytes. These results demonstrate that Leishmania infection did not interfere with VLA4-mediated monocyte rolling or initial binding to fibronectin
This decrease in leukocyte adhesion correlated with the parasite burden in these mononuclear phagocytes and was reversed by integrin activation with Mn++5
Summary
Infection with Leishmania downregulates the expression of the genes encoding the chemokine receptors CCR4 and CCR5 in murine inflammatory macrophages and the genes encoding CCR2 and CCR5 in murine dendritic cells[5,6]. The function of VLA4, a β 1 integrin involved in leukocyte adhesion to fibronectin, is modulated by Leishmania infection[5]. This molecule may be present on the leukocyte surface in different conformations, and it mediates rolling or firm adherence of the cell to the substrate[8]. When macrophages adhere firmly to the substrate, they spread extensively. This spreading stabilizes the adherence and allows cell haptotaxis toward increasing chemokine concentrations[9]. We examine the effect of Leishmania infection on the rolling and spreading of infected monocytes over fibronectin. We used a reporter antibody to study the affinity state of the VLA4 expressed by infected and uninfected monocytes
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